1. Field of the Invention
This invention relates to methods for optical stabilization and movement compensation to improve the accuracy of small arms and similar systems.
2. Description of Related Art
A significant limitation of shooting accuracy is presented by unsteadiness of the firearm. Bench-rest competition shooters employ stable platforms for their rifles to remove this source of motion. However, most other shooters must be content with imperfect supports for their firearms. For example, a standing shooter hand-holding a rifle results in a relatively unstable condition, and most shooters place the rifle in contact with a fixed object, such as a tree, bipod, or other stable platform. With accurate rifles capable of accuracies of better than one minute of angle or about one inch per hundred yards, even slight movements of the rifle can lead to inaccuracies far in excess of the capability of the rifle. Even a shift of only 0.01 inch by the muzzle of the rifle can generate a significant inaccuracy in perfect shooting conditions. Moreover, factors such as wind, the shooter's breathing, and heartbeat can generate deviations in aim which will adversely affect the point of impact of the bullet. In a combat or hunting context, the shooter's physiological responses to stress or excitement can significantly worsen the motion associated with holding an imperfectly-supported rifle.
The motion or shake that causes shooting inaccuracy also presents a visual problem. High-powered riflescopes magnify the motion, thus blurring the image. This makes it difficult to detect, acquire, and identify targets. Oftentimes, a shooter might prefer a higher-powered rifle scope for accuracy, except that the shaky image in actual use makes such higher magnification impractical. Additionally, the effect of mirage produced by atmospheric convection currents viewed over large distances can further complicate the aiming process and introduce undesirable inaccuracies.
With respect to difficulties in image clarity and movement, optical stabilization for cameras and binoculars has seen great commercial success. Moving a lens to keep the image stable and centered as the device moves greatly improves these optical devices. These moving lens techniques are very reliable, inexpensive, and lightweight with low power requirements. Such optical stabilization would be helpful to a shooter as he attempts to identify and prepare to shoot at a target. However, when it comes to improving accuracy, there are no viable optical stabilizers for small arms, such as rifles and pistols, because although the image is stable, the lens train and the barrel continue to move. In practice, the shooter quickly identifies his target and centers the target in the stabilized image, but he still has no way of knowing when the barrel is aligned with the target. The barrel continues to move relative to the stabilized image due to unsteadiness in the position due to involuntary factors such as heartbeat, breathing, and muscular activity.
Specifically, a bullet fired at the precise instant that the moving barrel is exactly aligned with the target will always miss the target. Under those conditions, the moving barrel necessarily imparts movement to the bullet that will carry it away from the target. Skilled shooters sometimes acquire a rhythmic pattern with the barrel and pull the trigger at the right moment for the imparted barrel motion to bring the bullet into contact with the target when it arrives. Many hours on the range give them the “feel” for this effort at different ranges, but it is an imprecise solution to barrel movement, reflecting the need to compensate for movement that can never be completely eliminated. Ideally, a barrel movement compensation system, such as that presented herein, could track the position of the barrel relative to the stabilized image, and then release the firing mechanism at a calculated moment for the bullet to contact the target at the end of its flight. The result would be greater accuracy, as well as easier identification and alignment with the target prior to taking the shot.
Many attempts have been made to increase the accuracy of weapons, from small arms to heavy artillery. For weapon systems where optical acuity, bulk, weight, and power consumption do not appear to be concerns, it has been proposed to employ a gyroscopically-stabilized television image as a fire-control sighting system for a weapon on a moving platform to provide a still image. This is described in U.S. Pat. No. 3,659,494 to Philbrick et al. The Philbrick system projects an image of the target on a photodetector, which converts the image into an electronic signal. An electron beam regenerates the image on a phosphor screen that is viewed by the user. The regenerated image is stabilized by a facility that shifts the electron beam based on gyroscopic inputs. While apparently suitable for aiming large weapon systems, it does not appear to be suitable for applications where a high quality image, and small size, low weight, low cost, and simplicity are desired. Moreover, it appears unsuited to adapt to existing rifle scopes.
The Philbrick patent further describes the system applied to a weapon with an electronic trigger system, so that the sighting system itself automatically sends an electronic signal that fires the weapon when the sight is in a neutral or “home” position in which the image is not shifted, unless the user inhibits firing by releasing pressure on a trigger solenoid. Thus, the Philbrick system is further unsuitable for adaptation to convention rifles using mechanical triggers.
The present invention addresses all of the foregoing concerns and difficulties attributable to movement of the firearm. By controlling the release of the firing mechanism instead of firing at the right position, the invention eliminates complex controls required with systems that directly operate the firearm. In other words, the firearm will only fire under the simultaneous occurrence of two conditions: (1) the trigger is pulled, and (2) a release signal is received from the compensation system upon a calculation that the bullet will intersect the target at the end of its time of flight. This method allows the shooter to identify and aim with a stable image of the target using a conventional optical stabilization system, select that target by pulling the trigger, and the system releases the firing mechanism when the motion of the barrel imparts the correct motion to the bullet so that it contacts the target at the end of its time of flight using information from that same optical stabilization system.
Thus, the present invention provides an inexpensive and simple way to overcome the otherwise unavoidable problems due to movement of the shooter and the firearm. Also, the invention resolves issues that have historically kept optical stabilization out of the small arms market.